In a typical imaging system, an image beam is directed through a lens and onto an image sensor, for example a CCD (Charge Coupled Device), comprised of an array of sensing elements. These sensing elements, generally referred to as "picture elements" or "pixels", are arranged in rows and columns. As the array is scanned, the electrical output signal from each pixel is processed and used to produce a display, for example on a television monitor. Therefore, the resolution of such a display is a direct function of the number of pixels in the array of rows and columns. For example, an image sensor having 500 horizontal pixels per row will have a lower resolution than an image sensor which has 1,000 pixels per row. Increasing the number of pixels will increase the resolution. However, this will also increase the size of the image sensor. Therefore, other methods are sought to increase the resolution of an image without increasing the size of the image sensor.
One method is to scan the array multiple times while shifting the position of the image with respect to the image sensor between each scan. By shifting the image position, each pixel of the image sensor will capture information on several adjacent areas of the image. Thus, a low resolution array can be used to produce a high resolution image.
U.S. Pat. No. 4,920,418, "Imaging System Having a Swing-Driven Image Sensor" by Robinson discloses an apparatus for improving the resolution and reducing the optical alias of interlaced imaging systems which include a solid state image sensor. In one embodiment, the apparatus comprises a glass plate mounted on piezoelectric bimorphs. When a voltage is applied, the bimorphs tilt the glass plate between two positions corresponding to two fields such that the image passing through the glass plate is shifted relative to an image sensor. The images are scanned by the image sensor and the resulting signals are interlaced to form an image.
In U.S. Pat. No. 4,581,649, "Image Pickup System" by Morokawa, an image system is disclosed. The image system has an image sensor which includes a plurality of photodetectors arranged in two dimensions and an optical system having a lens for forming an image on the image sensor so that the image sensor produces picture data. A vibrator, comprising a pair of piezoelectric vibrator elements, is provided for vibrating the image on the image sensor so as to oscillate the picture data. A scanner is provided to be operative in synchronism with the vibration of the image for changing the oscillated picture data to data for a fixed image.
U.S. Pat. No. 4,755,876, "Image Scanner" by Dangler, discloses and image scanner which utilizes a dither plate to steer an image onto a sparsely-populated image sensor. Precisely controlled motors are used to properly position a pair of dither plates mounted for movement on orthogonal axes to provide "X" and "Y" scan directions.
U.S. Pat. No. 4,633,317, "Electro-Optical Detector System" by Uwira et al, discloses a high resolution electro-optical detector having a mosaic CCD. The CCD is configured as a sparse array of sensing elements separated by interstices. A mirror, suspended on gimbals, is electro-magnetically energized to periodically displace the image in a stepwise manner along a closed rectangular trajectory. The displacement allows the sensing elements to capture image information which would otherwise intersect the interstices. In further embodiments, the image is offset by rotating an optical component, such as an optical wedge or inclined optical plate.
U.S. Pat. No. 4,967,264, "Color Sequential Optical Offset Image Sampling System" by Parulski et al, discloses an image system incorporating multiple glass plates mounted at angles on a rotating filter wheel. The glass plates are positioned so as to displace a beam of light by a specific distance, each in a different direction. The image sensor's pixels sequentially receive the light passing through each of the filters and converts the image formed by the light to corresponding electrical signals. The electrical signals from each image are reordered by interleaving, to form an image with increased resolution.
The precisely controlled motors used by Dangler and the piezo-electric elements used by Robinson and Morokawa are expensive components which are not appropriate for a high quantity and/or low cost system. Furthermore, the high voltage requirements of the piezo-electric elements may not be desirable for consumer products. Size constraints indicate that the magnetically energized mirror of Uwira et al may not be suitable in compact devices. In addition, the apparatus of Uwira et al comprising a rotating optical component is susceptible to aberrations in the optics. Parulski et al's filter wheel requires uniformity of the multiple glass plates. Therefore, though each of these inventions have achieved a certain degree of success, a need continues to exist for an image displacement mechanism which is robust, compact in size, inexpensive and simple to manufacture, and is insensitive to glass aberrations.